1. Field of Invention
The present invention relates to a remediation technology for organic contaminated soil, and more particularly to a system and method of remediation of organic contaminated soil.
2. Description of Related Arts
Electrokinetic remediation of organic contaminated soil relates to technology of reinforced remediation which is developed in the 90's in the 20 century in which inert electrodes are inserted in the contaminated soil to create a DC electric field. The electrical interactions increase an activity level of microorganisms through which the remediation elements are improved and the rate of degradation of contaminants is increased. Compared to other remediation methods, electrokinetic remediation method is advantageous in providing high efficiency and high safety level.
Electrokinetic remediation of organic contaminated soil has two major limitations. First, imbalance pH value in the soil is caused by a process of acidification of anode. The reason is that after a DC electric field is applied, oxidation reduction reaction becomes feasible for water around the electrode and hence H+ and OH− ions are resulted and accumulated around the anode area and cathode area respectively, creating two zones for the acid and alkaline respectively. Accordingly, the soil is separated into two areas, the acid area and the alkaline area, which in turn decreases the activity level of the microorganisms in the soil and hence lowered the efficiency of removing contaminants. Second, the usable area percentage of the electrical field is relatively low, therefore the efficiency of removing contaminants is lowered. Different grid patterns or alignments are employed to solve this problem but the major problem of having a high percentage of non-usable area is not solved. On the other hand, the usable area in the field, the strength of electric field and the efficiency of degradation of contaminants are interrelated and are positively correlated.
In order to solve the problem of anode acidification, control methods such as bridging the two electrodes with electrolytes (Lee and Yang, 2000); adding cation exchange membrane (Li et al., 1998); adding buffer solution around the two zoned areas (Saichek et al. 2003); and applying electrodes to control a change of soil pH (Shen et al. 2007) are proposed. These methods is able to solve anode acidification at some level, but their applications are complicated, difficult to monitor, and costly in general. In order to increase the percentage of usable area for electrokinetic process, conventional method includes one-dimensional/two-dimensional electrode grid and two-ways operation process (Wang Wai et al. 2006). However, since the two adjacently positioned electrodes always have the same polarity under the two-ways operation process, dead corners are created and hence the percentage of usable area is still very low.